Printed circuit (PC) boards have found increasing application in electrical and electronic equipment of all kinds. The electrical circuits formed on these PC boards, like larger scale, conventional electrical circuits, need protection against electrical overloads. This protection is typically provided by subminiature fuses that are physically secured to the PC board.
One example of such a subminiature, surface-mounted fuse is disclosed in U.S. Pat. No. 5,166,656 ('656 patent). The fusible link of this surface-mounted fuse is disclosed as being covered with a three layer composite which includes a passivation layer, an insulating cover, and an epoxy layer to bond the passivation layer to the insulating cover. See '656 patent, column 6, lines 4-7. Typically, the passivation layer is either chemically vapor-deposited silica or a thick layer of printed glass. See '656 patent, column 3, lines 39-41. The insulating cover may be a glass cover. See '656 patent, column 4, lines 43-46.
Another prior art device is described in U.S. Pat. No. 5,552,757. In that invention, unlike the '656 patent, the fusible link is protected with only one, rather than three, layers. In the '757 patent, however, this one protective layer 56 is a polycarbonate adhesive or the like. This protective layer 56 extended substantially above the general borders of the surface-mount fuse shown in FIG. 12 of the '757 patent. As a result, the fuse shown in FIG. 12 of the '757 patent could only be placed on a circuit board with the protective layer 56 facing upwardly, away from the board.